The present invention relates to the field of mass storage devices. More particularly, this invention relates to a method of characterizing a disc drive stiction/fiiction during the disc drive spin-up.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer head to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer head is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of disc drive. Servo feedback information is used to accurately locate the transducer head. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
The actuator/arm is rotatably attached to a shaft via a bearing cartridge which generally includes one or more sets of ball bearings. The shaft/post is attached to the base and may be attached to the top cover of the disc drive. A yoke is attached to the actuator. The voice coil is attached to the yoke at one end of the rotary actuator. The voice coil is part of a voice coil motor which is used to rotate the actuator and the attached transducer or transducers. A permanent magnet is attached to the base and cover of the disc drive. The voice coil motor which drives the rotary actuator comprises the voice coil and the permanent magnet. The voice coil is attached to the rotary actuator and the permanent magnet is fixed on the base. A yoke is generally used to attach the permanent magnet to the base and to direct the flux of the permanent magnet. Since the voice coil sandwiched between the magnet and yoke assembly is subjected to magnetic fields, electricity can be applied to the voice coil to drive it so as to position the transducers at a target track.
Tribological qualifications of the head-disc interface is generally a critical path to final qualification of both the head and the disc during the design and development stage of new disc drives. Current methods to measure stiction and friction between the head and the disc during the disc drive spin-up are generally intrusive and very time-consuming. This can result in considerable loss of time during the design and development stage of the disc drives. Currently there is no non-intrusive and reliable method of characterizing stiction and friction between the head and the disc during the disc drive spin-up. Current methods require significant drive and connection modifications to make these measurements. Almost all of the existing methods to quantify stiction and friction require removing the top-cover of the disc drive to make these measurements. In addition to removing the top cover of the disc drive assembly, one method requires attaching a string to the spindle motor, and pulling a string with a strain gauge while holding the drive stationary. The output of the strain gauge is recorded via a strip chart recorder to quantify the stiction and friction forces. Most other current methods for characterizing stiction and friction between the head and the disc require significant disc drive modifications before making any measurement. One such method includes spinning the disc drive about its spindle-motor z-axis, and measuring the rotational acceleration point at which stiction and friction values are exceeded. This method requires time-consuming hardware mounting and disc drive balancing of each disc drive in the measurement apparatus. Another method requires measuring motor current at which the disc drive breaks free of the head and-disc contact (stiction and friction) and begins to spin. This method requires the connection of a special disc drive circuitry to measure and output the breakaway motor current. Also this special disc drive circuitry must be configured and calibrated for each product independently before making any measurements. All of these current methods to characterize stiction and friction between the head and the disc are intrusive and time-consuming. Also these methods raise potential handling and contamination issues for disc drive assemblies, which are generally hermetically sealed.
What is needed is a reliable non-intrusive method to characterize stiction and friction between a head and a disc during a disc drive spin-up for disc drive assemblies, that is not time consuming, that does not require modifications to disc drive assemblies, and that does not raise any handling and contamination issues.
A disc drive includes a base, and a disc rotatably attached to the base. The disc drive also includes an actuator assembly rotatably attached to the base, and a device for moving the actuator assembly. The actuator assembly includes an arm carrying a transducer head in a transducing relationship with respect to the disc. The disc drive further includes a servo circuitry and a controller for controlling movement of the actuator assembly during a track follow and a track seek. Piezoelectric transducers are attached to the actuator assembly for measuring stiction and friction forces developed between the transducer head and the disc during a disc drive spin-up. In one embodiment the piezoelectric transducers are part of the actuator assembly. The disc drive further includes an internal lead, coupled to piezoelectric transducers on one end and, and disposed to extend outside the disc drive on other end for non-intrusive coupling with an external processor. During a disc drive spin-up, signals generated by the piezoelectric transducers are received by the external processor through the internal lead, and analyzed to characterize the stiction and friction forces developed between the transducer head and the disc.
Advantageously, the non-intrusive method of characterizing the stiction and friction forces developed between the transducer head and the disc during the disc drive spin-up set forth above, and the apparatus for implementing the above non-intrusive measurement procedure, allow for making faster measurements and virtually eliminate any potential handling and contamination issues that can occur in current intrusive methods of making the stiction and friction measurements. The end result will be a method of characterizing stiction and friction in a disc drive, that is non-intrusive, that is not time consuming, that does not require modifications to disc drive, and that does not raise any potential handling and contamination issues during stiction and friction measurements.